Field of the Invention
The invention relates to a circuit arrangement for revealing errors in the case of a light signal, particularly for railway safety installations, having an electronic signal transmitter, which disconnects itself reversibly in the event of an error, and an actuating part, designed for incandescent lamps, for actuating and monitoring the signal transmitter, wherein the revelation of errors comprises error differentiation between line-conditioned influencing voltage and errors in the signal transmitter.
The description below relates essentially to light signals for railway safety installations, without the invention being limited to this application. Rather, application is also conceivable from other traffic systems or in the industrial sector, for example.
In the case of incandescent lamp light signals, the lines are dimensioned such that influencing the signal wires prompts the influencing current to flow through the incandescent lamp and this influencing current does not result in the incandescent lamp lighting. Actuating parts that are designed for incandescent lamp light signals usually evaluate a signal current in order to establish an error or correct operation of the light signal.
When incandescent lamp signal transmitters are replaced by electronic signal transmitters, for example for LED light sources, the influencing current results in the electronics working but the low energy for the influencing meaning that it is not possible to start the signal transmitter. The signal voltage falls upon a starting attempt and the signal transmitter that disconnects itself reversibly begins the next starting attempt.
This starting procedure is also effective when there is a low-impedance error in the signal transmitter. The impedance of the signal line causes the signal voltage to collapse when the electronics are engaged. In this case, a very large current flows that the actuating part rates not as an error but rather as a valid signal current. By contrast, the electronics cannot measure the current on account of the low voltage and possibly begin a new starting attempt.
The same starting behavior for an error-free signal transmitter with influencing and a signal transmitter with a low-impedance error means that the cause of error cannot be identified. Therefore, it is necessary to ensure that the electronic signal transmitter can distinguish between signal transmitter voltage and influencing voltage in order to reveal not only the presence of an error but also the cause of error.
To date, this problem has been solved in that the actuating part identifies the error in the event of an excessively large flow of current and in that the signal transmitter identifies the error, and transmits it to the actuating part, in the event of only a slightly increased flow of current. This error revelation is not always assured in the event of relatively high impedances on the signal line, however, since there is a gap between the identification of current flow by the actuating part and the identification of current flow by the signal transmitter. This gap in the identification of current flow is closed by virtue of the signal transmitter evaluating the current immediately after the start, that is to say before the signal voltage collapses. This requires signal-transmitter-internal capacitors that are charged by the actuating part and supply the signal transmitter with current for a sufficiently long time. After the electronics of the signal transmitter with a low-impedance error have started, large currents can therefore be measured and used for error identification. A prerequisite is that the capacitors can store their energy for a sufficiently long time. The operation of the capacitors is usually not tested, however.